The study identifies the Thr1313Met mutation in the SCN4A gene as the cause of paramyotonia congenita in a Japanese family, a condition with very low prevalence in Japan.
May aid familial diagnosis in rare Japanese cases; leaves open population prevalence and therapeutic implications.
A 37-year-old Japanese woman was referred from another clinic to confirm the diagnosis of myotonia congenita. She had experienced cold-induced myotonia and muscle stiffness from early childhood. Of her three children, her elder son and her daughter have clinical features similar to hers. They experience neither grip nor percussion myotonia during warm weather, whereas myotonia is provoked by cold. Her younger son has no symptoms. DNA analyses of the SCN4A gene showed a C to T transition at nucleotide position 3938 in exon 22 of SCN4A (Thr1313Met) in all three affected family members, but not in the unaffected son. Paramyotonia congenita, the prevalence of which is very low in Japan, was diagnosed based on their clinical features and DNA analysis results.
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KlNOSHITA et al. (2003) studied this question.
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